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12.2 


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u  mil  1.6 


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Photographic 

Sciences 

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D 


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10X  14X  18X  22X 


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y 

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24X 


28X 


32X 


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IVIontreal 

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plua  grand  soin,  eompta  tanu  da  la  condition  at 
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conformiti  avac  las  cor.Miu^^ns  du  contrat  da 
filmaga. 


Original  copiaa  In  printad  papar  oovars  ara  fllmad 
beginning  with  tha  front  covar  and  anding  on 
tha  last  paga  with  a  printad  or  lilustratad  impraa- 
sion,  or  tha  back  covar  whan  appropriate.  All 
othar  original  copiaa  ara  filmed  beginning  on  the 
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or  illustrated  impression. 


The  last  recorded  frame  on  each  microfiche 
shall  contain  tha  symbol  •-»>  (meaning  "CON- 
TINUED"), or  tha  symbol  ▼  (meaning  "END"), 
whichever  applies. 


Les  exemplaires  originsux  dont  la  couvetture  en 
papier  eat  imprimte  sont  filmte  en  commei.ttant 
par  la  premier  plat  at  en  terminant  soit  par  la 
darnlAre  paga  qui  comporta  une  empreinte 
d'impreaaion  ou  d'liiustration.  soit  par  la  second 
plav  selon  le  cas.  Tous  les  autres  exemplaires 
origins  jx  sont  filmAs  en  comrnen^atM  par  la 
premiere  paga  qui  compryrta  une  em^Teinte 
d'impreaaion  ou  d'liiustration  at  an  tariT«inant  par 
la  darnlAre  page  qui  comporte  une  telle 
empreinte. 

Un  dee  symbules  suivanta  apparattra  sur  la 
darnlAre  image  de  cheque  microfiche,  selon  le 
caa:  la  symbols  -^  signifie  "A  SUiVRE".  le 
symbols  V  signifie  "FIN". 


Mapa,  plates,  charts,  etc.,  may  be  filmed  at 
different  reduction  ratios.  Those  too  large  to  be 
entirely  included  In  one  exposure  ara  filmed 
beginning  in  the  upper  left  hand  corner,  left  to 
right  and  top  to  bottom,  as  many  framea  aa 
required.  The  following  diagrams  illustrate  the 
method: 


Lee  cartaa.  planches,  tableaux,  etc..  peuvent  Atre 
filmis  A  dee  taux  de  reduction  diff Arents. 
Lorsque  le  document  e&t  trop  grand  pour  Atra 
reproduit  en  un  saui  clichA.  11  est  fiimA  A  partir 
da  Tangle  supArieur  gauche  da  gauche  h  droite. 
et  de  haut  an  baa,  en  prenant  le  nombre 
d'Imeges  nteessaire.  Les  diagrammas  suivanta 
illuatrent  la  mAthoda. 


1  2  3 


1 

2 

3 

4 

5 

6 

=  ^ 

:::n-.'3aiS!iaiHiH 


Color 


App 
the 


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M.i.i,,|.,„i„.,j„„i.,„i„„j„>„„i„„i;„,=|„,^,^||Jiiij|i! 


ism-ga'giMSJgiggaaasjiiamaiSg 


Color  Measurement,  and  its 
Application  in  Medicine  and 
the  Arts. 


BY 


CASEY  A.  WOOD,  M.D. 


Oft  THOMAS  A.  WOODRUFF. 

t<M  RCkMNCI  ILOQ., 

CHICAOa 


REPRINTED  PROM 
MBDICINE. 

OBO.  5.  DAVIS.  Publisher. 

March,  189^. 


■T  -<cijr<yi 


COLOR  MEAJ 


Professor 

For  some 

the  neglected 

versal  standar 

clature  havin 

England,  Frai 

names  continu 

reference  to  th 

The  recen 

many  new  shai 

a  study  of  nvx 

dye-stuffs  is  n 

Even  in  forma 

sionally  sees  s 

"  apple   blossoi 

gray,"  etc. 

The  metri( 

readings  for  tl: 

used  in  electri 

might  be  quotec 

supply  of  conv 

various  departn 

with  chromatics 

this  and  kindn 

better,  to  emplc 

penny  paint-box 

There  wou 

tific  nomenclatu: 

i-e.,  if  it  could  t 

tries.     Such,  ho 

compare  the  col 

French  dealers  \ 

stores  of  Americi 

more  or  less  loca 

tions — the  new  c 

countries,  but  di: 

the  catalogues  of 

issued  by  sellers 


\ 


[reprintkd  from  mkhicinr,  march  iRyfi.) 


!? 


COLOR  MEASUREMENT,  AND  ITS  APPLICATION  IN  MEDICINE  AND 

THE   ARTS. 

BY  CASEY  A.  WOOD,  M.D.,  ' 

Professor  of  Ophthalniology  in  the  Post-Gmdiiate  Medical  School,  Chicago. 

For  some  reason  or  other,  chromonietry  continues  to  be  one  of 
the  neglected  sciences,  and  as  result  we  are,  even  in  this  age  of  uni 
versal  standards,  without  generally  accepted  color  units  or  a  nomen- 
clature having  a  scientific  basis.  Not  only  in  America,  but  in 
England,  France,  and  all  the  other  Continental  countries,  arbitrary 
names  continue  to  be  given  to  color  shades  and  mixtures,  without 
reference  to  their  spectral  or  other  value. 

The  recent  advances  in  the  art  of  dyeing  and  the  discovery  of  so 
many  new  shades  and  color  combinations  are  the  direct  outcome  of 
a  study  of  modern  chemistry;  and  yet  the  technology  of  dyeing  and 
dye-stuffs  is  not  comparable  in  definiteness  with  chemical  terms. 
Even  in  formal  treatises  on  stains,  paints,  and  pigments,  one  occa- 
sionally sees  such  absurd  color  designations  as  "oriental  drab," 
"apple  blossom,"  "Nile  green,"  "ashes  of  roses,"  "French 
gray,"  etc. 

The  metrical  system  of  weights  and  measures,  the  centigrade 
readings  for  the  thermometer,  the  comparatively  recent  notation 
used  in  electrical  measurements,  and  numerous  other  instances 
might  be  quoted  as  well  known  examples  of  the  demand  for  and  the 
supply  of  convenient  and  universal  standards  of  measurement  in 
various  departments  of  the  arts  and  sciences.  Quite  otherwise  is  it 
with  chromatics.  Even  the  most  scientific  and  exact  writer  upon 
this  and  kindred  subjects  must  continue,  for  want  of  something 
better,  to  employ  the  phraseology  of  the  bargain  counter  and  the 
penny  paint-box. 

There  would  not  be  so  much  room  for  criticism  of  this  unscien- 
tific nomenclature  if  it  were  a  constant  one  or  if  it  were  universal — 
i.  e. ,  if  it  could  be  translated  into  color  names  in  use  in  other  coun- 
tries. Such,  however,  is  by  no  means  the  case.  It  is  instructive  to 
compare  the  color  charts  to  be  seen  in  the  shops  of  German  and 
French  dealers  with  those  exposed  for  sale  in  the  artists'  material 
stores  of  America.  It  will  be  found  that  each  nation  has  its  own 
more  or  less  local  and  more  or  less  fanciful  names  for  color  combina- 
tions— the  new  ones  especially.  Not  only  is  this  true  of  different 
countries,  but  differences  in  color  nomenclature  are  often  found  in 
the  catalogues  of  dealers  in  paints  and  dyes,  as  well  as  in  color-cards 
issued  by  sellers  of  artists'  materials,  within  the  same  country.    The 


COLOR  MEASUREMENT 


' '  terra  cotta ' '  of  one  paint-manufacturer  is  not  necessarily  the  same 
color  mixture  sold  by  his  rivals  in  the  same  city.  A  comparison  of 
the  sample  color-cards  issued  by  such  representative  firms  as  Winsor 
&  Newton  in  England,  the  Johns  Manufacturing  Company  in  this 
country,  Paillard  in  France,  and  Schmincke  in  Germany,  at  once 
shows  this.  Hardly  a  color  named  on  the  card  of  one  firm  is  an 
exact  reproduction  of  a  color  sample  of  any  other.  Thus  the  French 
firm's  "  Terre  de  Stenne  br&lSe,"  the  German  "Gedrannie  Terre  di 
Sienna,"  and  the  English  and  American  "burnt  Sienna,"  all  con- 
tain varying  proportions  of  red.  In  the  same  way  Schmincke' s 
"El/enbeinschwarz"  is  blacker  than  Paillard' s  '^noir  dHvaire" 
while  Winsor  &  Newton's  "ivory  black"  is  pale  when  compared 
with  either  of  these. 

This  is  what  lyudwig  Fischer  *  says  about  the  chemical  consti- 
tution of  that  well  known  color,  "Van  Dyck  brown:"  "This  pig- 
ment consists  for  the  most  part  of  oxide  of  iron  and  aluminum 
silicate,  and  is  often  obtained  by  burning  yellow  ochre.  The  color 
shade  depends  upon  the  amount  of  heat  applied,  and  these  variations  in 
tint  have  gained  for  it  in  commerce  many  names,  such  as  Prussian 
red,  English  red,  Nuremberg  red,  Roman  ochre,  Italian  earth,  red 
ochre,  and  ocre  rouge.  The  genuine  Van  Dyck  brown,  which  the 
artist  whose  name  it  bears  loved  to  use,  is  said  by  him  to  have  been 
prepared  from  deposits  found  in  the  neighborhood  of  Cassel. ' ' 

The  so-called  " Schweinf urth  green"  has  as  many  different 
names  as  variations  in  its  yellow-g^een  color.  Fischer  (p.  32)  says 
it  is  known  in  the  German  paint-shops  under  at  least  twenty-one 
different  designations. 

At  least  two  investigators  —  Captain  Abney  and  Mr.  J.  W. 
Lovibond,  of  Salisbury,  England — have  suggested  a  rational  color 
measurement  as  part  of  an  attempt  to  resolve  all  colors,  shades  and 
tints  into  terms  of  certain  primary  colors  accepted  as  a  standard.  In 
the  case  of  Mr.  Lovibond  f  many  years  of  experiment  have  resulted 
in  the  perfection  of  an  instrument  called  by  him  the  ' '  tintometer, ' ' 
by  means  of  which  any  color  combination  can  be  read  off  in  terms  of 
blue,  yellow,  and  red.  The  chief  difficulties  encountered  by  one  who 
attempts  to  establish  a  standard  of  color  are  that  of  finding  a  pure 
white  for  purposes  of  comparison,  of  deciding  upon  an  illumination 
which  shall  be  fairly  constant,  and,  lastly,  of  choosing  the  colors 
which  are  to  act  as  standards. 

Captain  Abney  %  obtains  his  standard  white  by  isolating  a  beam 

♦  Die  Technick  der  Arquarell-Malerei,  p.  28. 

t  Measurement  of  Light  and  Colour  Sensations,  p.  133. 

X  See  hi?  Colour  Vision,  and  an  earlier  work  on  Colour  Measu  rement  and  Mixture,  pp. 


from  the  cei 
two-  or  thre 
surface  of  th 
beam— is  rec 


.«...''/.. 
..^J- 


color  to  be  ma 
illuminates  a  pie 
surface.  By  an 
are  used  for  mat 
the  beam. 

Abney's  late 
I,  and  described 


COLOR  MEASUREMENT  ,  3 

from  the  centre  of  an  electric  light.  This  beam  is  directed  into  a 
two-  or  three-prism  spectroscope,  and  the  light  reflected  from  the 
surface  of  the  first  prism-considered  to  be  half  of  the  impinging 
beam-is  received  on  a  mirror  which  reflects  it  for  illuminating  the 


..JR.! 


r; 


Mi 


V  nr.. 


ccaor  to  be  matched.     The  other  half,  as  a  prismatic  spectrum, 

lummates  a  piece  of  standard  white  paper  placed  beside  the  colored 

surtace     By  an  ingenious  shutter  arrangement  the  spectral  colors 

the  beam  '"^  ^""^  *^^"  determining  the  color  composition  of 

Abney's  latest  modification  of  his  instrument  is  shown  in  Fig 
I,  and  descnbed  on  pages  18-20  of  his  published  Tyndall  I^ectures: 


1^ 


COLOR  MEASUREMENT 


"R  R  are  rays  coining  from  the  source  of  light,  be  it  sunlight  or 
the  electric  liglU,  and  an  image  of  the  one  or  the  other  is  formed  by 
the  lens  Li  on  the  slit  Si  of  the  collimator  C.  The  parallel  rays 
produced  by  the  lens  L.i  are  partially  refracted  and  partially 
reflected.  The  former  pass  through  the  prisms  P,,  Pj,  and  are 
focused  to  form  a  spectrum  at  D  by  the  lens  Lg.  D  is  a  movable 
screen  in  which  is  an  aperture  S^,  the  width  of  which  can  be  varied 
as  desired.  The  rays  are  again  collected  by  a  lens,  L4 ,  and  form  a 
white  image  of  the  surface  of  the  last  prism  on  the  screen  E.  If  the 
light  passing  through  S2  is  alone  used,  the  image  at  E  is  formed 
practically  of  monochromatic  light.  Part  of  the  rays  falling  on  Pj 
are,  as  just  said,  reflected,  but  as  it  and  the  refracted  part  are  por- 
tions of  the  light  pa.ssing  through  the  slit  Si,  they  both  must  vary 
proportionally.  If  then  we  use  the  reflected  portion  as  a  com- 
parison light  to  the  spectrum  colors,  the  relative  intensities  of  the 
two,  though  they  may  vary  intrinsically  will  remain  the  same.  The 
rays  reflected  from  Pi  fall  on  G,  a  silver  or  glass  mirror,  and  by 
means  of  another  lens,  Iv,,,  also  can  be  caused  to  form  a  white  patch 
on  the  screen  E,  alongside  the  patch  of  color.  At  M,  or  anywhere 
in  the  path  of  the  beams,  an  electro-motor  driving  a  sector  with 
apertures  which  can  be  opened  or  closed  whilst  rotating,  is  placed, 
and  the  illumination  of  either  beam  can  be  altered  at  will.  To 
obtain  a  large  spectrum  on  the  screen  E,  all  that  is  necessary  is  to 
interpose  a  lens  of  fairly  short  focus  in  front  of  Iy4,  when  a  spectrum 
of  great  purity  and  brightness  can  be  formed. ' ' 

In  the  lyovibond  instrument  the  depth  of  color  in  liquids  and 
solids  can  be  accurately  measured  in  degrees,  placed  in  their  position 
in  a  penuanent  color  scale,  and  registered.  The  instrument  consists 
(see  Figs.  2,  3,  4,  and  5)  of  a  graded  series  of  standards,  made  of 
colored  glasses,  numbered  according  to  their  depth  of  color,  and  an 
instrument  for  holding  the  glasses  and  the  object  to  be  measured. 
Only  three  color  scales  are  necessary  for  investigation  work;  these 
are  red,  yellow,  and  blue;  but  for  some  special  purposes,  such  as  for 
brewers,  for  the  estimation  of  carbon  in  steel,  for  urinalysis,  etc., 
scales  in  other  colors  are  found  convenient.  Each  ordinary  scale 
consists  of  glass  slips  all  of  one  color  but  differing  in  depth,  the 
divisions  of  difference  being  regular,  forming  degrees  or  units  as  in 
the  case  of  temperature  degrees  on  a  thermometer  scale,  or  inches 
on  a  foot-rule. 

The  color  units  are  not  only  of  equal  depth  throughout  each 
scale,  but  have  also  a  color  equivalence  in  relation  to  each  other; 
that  is,  a  given  number  of  units  in  one  scale  has  an  equivalence  of 


m^MWi 


■HWi   tSi!   ■,    ^  i    m.i 


COLOR  MEASUREMENT  ,  5 

color  value  in  relation  to  the  :->aine  imniher  of  units  in  the  other  two 
scales,  so  that  ajxin  combinations  of  ecjual  units  of  any  two  or  of  the 
three  a  color  nomenclature  is  founded  which  consists  of  eight  funda- 
mental terms  by  means  of  which  every  possible  color  can  be  first 
measured  and  theti  described. 

The  instrumf  nt  consists  essentially  of  a  double,  parallel-sided, 
wooden  tube,  ending' in  an  eye-piece  at  one  end,  and  equal  apertures 
for  viewing  the  color  to  be  measured  and  for  the  glasses  used  as 
measurers  at  the  other  end.  Provision  is  made  for  the  equal  illumi- 
nation of  the  color  to  be  measured  and  the  standard  white  or 
reflector  from  which  the  light  is  conveyed  to  the  comparison  tube; 
and  also  for  the  easy  adjustment  of  the  gla.sses  used  in  the  measure- 
ments. The  mechanism  also  avoids  the  side  lights  (falling  on  the 
eyes)  which  often  render  the  critical  estimation  of  color  under  ordi- 
nary conditions  of  observation  absolutely  impossible.  Both  fields  of 
view  are  evenly  illuminated  with  indirect  sunlight.  When  this  is 
effected,  either  side  can  be  used  for  the  standard  white  without 
affecting  the  measurement. 

The  colored  light  from  the  object  to  be  measured  is  transmitted 
through  one  tube,  and  the  light  from  a  standard  white  through  the 
other;  this  standard  white  light  is  then  intercepted  by  the  graded 
color  glasses  until  it  corresponds  in  color  to  the  object  to  be  meas- 
ured, when  the  numerical  color  value  of  the  glasses  used  can  be  read 
off.  I  append  a  desciiption  of  the  accompanying  cuts,  from  I,ovi- 
bond's  book: 

"A  longitudinal  section  of  the  instrument  is  shown  in  Fig.  2, 
which  consists  of  a  rectangular  tube  about  ten  inches  long,  divided 


Fig.lL 


in  the  middle  by  a  taper  partition,  B,  terminating  in  a  knife-edge  at 
the  eye-piece  C,  the  aperture  of  which  it  divides  into  two  equal 
parts.     This  cell  is  represented  crosswise  in  aperture. 

"At  the  other  end  are  two  openings,  A,  A,  which  admit  two 
equal  but  separate  beams  of  light  to  the  eye-piece  in  such  a  manner 
that,  on  looking  through  it,  the  eye  commands  a  simultaneous  dis- 
tinct view  of  both  openings.  The  knife-edge  of  the  partition,  being 
inside  the  range  of  vision,  does  not  disturb  this  distinctness  of  view. 


COLOR  MEASUREMENT 


The  grooves,  D,  D,  are  intended  to  receive  the  graded  sHps  of 
colored  glass  for  intercepting  the  beams  of  light  transmitted  through 
the  tubes  before  reaching  the  eye. 

' '  The  opening  at  I'^  is  intended  to  receive  the  gauged  vessel 
containing  the  colored  liquid  to  be  nieasured. 


"Fig.  3  represents  the  instrument  as  arranged  for  measuring 
color  in  liquids  up  to  two  inches  in  thickness.  The  optical  instru- 
ment, D,  slides  into  the  upright  stand  at  A,  to  receive  the  gauged 


cells  at  H  on  either  side.  Light  is  taken  from  the  standard  white 
reflector,  D,  on  st  d  D  B  C,  for  transmission  through  the  tubes  to 
the  eye- piece. 


COLOR  MEASdREMEN'l 


"A  separate  stand  is  required  for  cells  which  are  longer  thai- 
two  inches.  The  nietho<l  of  arrangement  is  shown  in  I-'ig.  4  where 
otie  end  of  the  longer  cell  rests  on  the  stand  A,  which  also  car- 
ries the  optical  instrument  B,  whilst  the  other  is  supix>rted  by  a 
separate  stand,  K,  which  can  be  moved  to  accommodate  a  tul)e  of 
any  length.     The  reflector,  I),  is  u.sed  as  in  Kig.  •?. 

"Fig  5  shows  the  arrangement  for  measuring  color  in  opaque 
objects.     The  optical  instrument,  B,  is  here  shown  as  a  binocular, 


but  the  monocular  described  in  Fig.  3  fits  equally  well  into  the  shoe 
A  ,  the  bottom  of  which  is  commanded  by  both  tubes  of  the  instru- 
ment. Under  one  side,  at  F,  is  placed  the  opaque  substance  to  be 
measured,  and  under  the  other  the  standard  white  (pure  precipitated 
lime  sulphate  pressed  to  an  even  surface)  for  reflecting  the  beam  of 
white  light,  which  is  then  intersected  at  J  by  the  suitable  standard 
glasses,  as  already  described  for  transparent  colors." 

At  my  request  the  inventor  of  this  valuable  instrument  has 

measured  a  number  of  pigment  samples  selected  at  random  from  the 

stock  of  a  large  American  color  and  paint  manufacturer.     I  give  the 

results  in  a  few  cases:  The  paint  sold  under  the  name  of  "prim-  f 

rose  'was  found  to  contain  1.16  red  units,  2.9  yellow  units,  and  .04 

ofablueumt;  the  so-called  "sahnon  "  color  equals  1.3  units  of  red,  •     j 

2.7  of  yellow,  and  1.5  of  blue;  "llac"  equals  red  1.85,  yellow  1.7,  | 

and  blue  3  units;  ' '  green  stone ' '  is  composed  of  red  i .  3,  yellow  27  * 

andblue  1.5  units;   "  apple  blossom  "  is  composed  of  red  1.9,  yellow  J 

.95.  blue  .8;  "  light  blue  "  is  composed  of  red  .95,  yellow  1.2,  blue  I 

4.9;     ^cream"  comprises  red  1.25,  yellow  2.5.  blue  .04;  "yellow 

stone,     red  4.3,  yellow  3.4,  blue  1.5;  "dark  drab,"  red  6.2,  yellow  I 

7.  blue  7;    "extra  light"  drab,  red   1.25,   yellow   1.35,   blue  2.8; 

golden  brown."  red  7.4,  yellow  7.4,  blue  3.2 


8 


COLOR  MEASUREMENT 


I  would  suggest  that  in  giving  the  composition  of  a  color  we 
write  it  like  a  chemical  formula:  for  instance,  "golden  brown" 
might  be  indicated  as  follows,  R7.4Y7.4B;,.2.  As  L,ovibond*  points 
out,  many  of  these  formulas  are  capable  of  reduction  to  simpler 
terms,  but  for  all  practical  purposes  it  is,  perhaps,  as  well  to  speak 
of  them  in  terms  of  the  primary  colors  accepted  as  standards. 

The  purposes  for  which  the  tintometer  is  now  used  are  numer- 
ous and  embrace  almost  every  department  of  the  arts.  A  few  of 
these  may  be  mentioned: 

It  has  been  found  that  the  amount  and  kind  of  adulteration  in 
most  foods  and  commercial  products,  as  well  as  the  impurities  com- 
monly found  in  drinking-water  and  other  fluids,  can  be  determined 
by  the  deviation,  measured  by  the  tintometer,  from  the  normal  tint 
of  the  pure  article.  Instead  of  making  a  laborious  and  complicated 
chemical  examination  of  the  suspected  compound,  its  color  value  is 
determined  in  a  few  minutes.  Such  a  chromometric  examination  is 
usually  found  to  answer  all  the  purposes  of  a  quantitative  analysis. 
In  this  way  the  tintometer  is  now  employed  in  England,  and  to 
some  extent  elsewhere,  by  all  sorts  of  conmiercial  houses,  and  it  is 
also  used  with  great  success  by  the  health  departments  of  cities  for 
the  ready  detection  of  impurities  and  adulterations  in  milk,  water, 
beer,  and  other  foods.  The  slightest  departure  from  purity,  whether 
in  food  or  any  other  product,  is  at  once  shown  by  a  measurable 
and  corresponding  variation  in  color. 

The  substitution  of  an  exact  color  measurement  for  a  chemical 
analysis  is  not  new  in  physics.  For  example,  the  Bessemer  process 
of  converting  iron  into  steel  is  almost  entirely  regulated  by  color 
changes  observed  in  the  furnace  flame.  It  is  exactly  on  this 
principle,  except  that  the  examination  is  made  leisurely,  that  in  a 
mixture  or  solution  any  departure  from  the  standard,  both  as  to 
kind  and  amount,  is  estimated  by  this  instrument.  When  an  exact 
color  measurement  has  been  made  of  a  certain  product  (it  matters 
not  whether  it  be  liquid  or  solid),  the  tintometer  very  readily  shows 
whether  a  commercial  sample  is  of  equal  purity. 

To  a  limited  extent  chromometry  has  also  been  made  use  of  for 
diagnostic  purposes  in  medicine.  In  urinary  analysis  we  have  the 
Vogel  scale  of  colors,  where  variations  from  the  tint  exhibited  by 
normal  urine  are  intended  to  indicate  something  of  the  chemical 
composition  of  that  excretion. 

The  best  example,  however,  of  the  use  of  a  chromometer  as  an 
aid  to  medical  diagnosis  is  the  hemoglobinometer,  by  which  color- 

♦  Measurement  of  tight  and  Colour,  p.  39. 


changes  in 
certain   im] 
normal  bloc 
blood  unde 
it  correspoi 
exactly  con 
blood.     In 
which  I  ia 
urer  of  abnc 
Gower's  to 
exact  chron 
in  1885.     H 
the  shade  o 
movement  i 
under  exam 
off  the  side 
ment  for  chr 
The  att 
Fleischel  ins 
I/Ovibond's  € 
ored  glass," 
in  glass  of  \ 
ground  and 
vessels  were 
arranged  to 
right-angles 
line  to  read 
color  match  \ 
the  thickness 
liquids  prove 
"An  inci 
concerning  th 
ing  colors,  o\ 
without  a  bre 
to  arrive  at 
blending,  wa; 
person  may  i 
point   by   the 
entirely  to  re 
standards;  th( 
ard-glass  slip 
minute  shades- 


i^^mvw^pn 


COLOR  MEASUREMENT 


"^ 


changes  in  the  blood,  pointing  to  an  excess  of  or  a  diminution  in 
certain  important  constituents,  are  measured  by  reference  to  a 
normal  blood  color  taken  as  a  standard.  In  Gower's  instrument  the 
blood  under  examination  is  diluted  with  water,  drop  by  drop,  until 
it  corresponds  in  color  to  that  of  a  tube  of  red  fluid  assumed  to 
exactly  correspond  in  shade  with  a  one-per-cent.  solution  of  normal 
blood.  In  practice  this  little  instrument  presents  several  defects, 
which  I  intend,  later  on,  to  point  out.  A  more  pretentious  meas- 
urer of  abnormal  blood,  and  one  which  conforms  more  closely  than 
Gower's  to  those  conditions  that  have  been  found  necessary  for 
exact  chromometry,  is  that  of  Fleischel  von  Marxow,  first  patented 
in  1885.  Here  the  blood  is  compared  with  a  standard  ruby  glass, 
the  shade  of  which  is  increased  or  diminished  by  a  simple  screw 
movement  until  it  corresponds  in  color  with  the  blood  mixture 
under  examination.  The  absence  of  any  arrangement  for  cutting 
off  the  side  lights  appears  to  me  to  reduce  the  value  of  this  instru- 
ment for  chromometric  purposes. 

The  attempt  to  compare  the  standard  glass  now  used  in  the 
Fleischel  instrument  with  blood  samples  is  beset  with  difficulties, 
lyovibond's  early  experiments  {loco  cii.,  p.  14)  showed  this.  "Col- 
ored glass,"  he  says,  "  was  next  tried,  and  long  rectangular  wedges 
in  glass  of  different  colors,  with  gradually  graded  tapers,  were 
ground  and  polished  for  standards,  whilst  corresponding  tapered 
vessels  were  made  for  the  liquids  to  be  measured.  These  were 
arranged  to  work,  at  the  end  of  the  instrument,  up  and  down  at 
right-angles  before  two  apertures,  s^de  by  side,  with  a  fixed  centre 
line  to  read  off  the  thickness  of  each  before  the  aperture  when  a 
color  match  was  made;  but  here  also  the  difference  of  ratio  between 
the  thickness  and  color  depth  of  the  different  colored  glass  and 
liquids  proved  fatal  to  the  method. 

"An  incidental  observation  was  made  during  these  experiments 
concerning  the  difficulty  of  arriving  at  a  final  judgment  with  taper- 
ing colors,  owing  to  one  shade  gradually  blending  into  the  next 
without  a  break  of  any  kind  to  arrest  the  vision.  The  mental  effort 
to  arrive  at  a  decision,  under  these  conditions  of  gradual  color- 
blending,  was  troublesome  and  vexatious  in  the  extreme.  Any 
person  may  realize  this  difficulty  by  attempting  to  fix  a  definite 
point  by  the  vision  in  a  graduated  color  line.  I  was  enabled 
entirely  to  remove  the  difficulty  by  using  separate  glass  slips  for 
standards;  the  line  of  color  decision  made  by  each  additional  stand- 
ard-glass slip  used  being  a  precise  definition  between  the  most 
minute  shades. ' ' 


10 


COLOR  MEASUREMENT 


I  am  myself  now  engaged  in  experimenting  with  a  hemometer, 
constructed  on  the  same  lines  as  the  tintometer,  which  I  shall  intro- 
duce to  the  profession  shortly  if  I  find  it  of  any  especial  value. 

A  rather  curious  application  of  the  tintometer  has  been  made  in 
a  certain  Agricultural  Experiment  Station  where  the  value  of  fertil- 
izers under  examination  is  determined  by  the  change  in  color  pro- 
duced in  the  leaves  of  certain  plants  whose  growth  was  used  as 
a  test. 

The  degree  of  dryness,  as  well  as  the  amount  of  yellow,  in 
samples  of  white  lead,  can  be  accurately  measured  chromometri- 
cally,  while  the  analysis  of  natural  waters  is  after  a  few  trials  made 
exceedingly  simple,  from  the  fact  that  the  amount  and  kind  of 
impurities  in  them  bear  a  fixed  relation  to  their  color.  So  it  is 
with  flour,  glucose,  indigo,  annatto,  lard,  butter,  chlorophyll,  steel, 
petroleum,  wine,  glycerin,  and  a  hundred  other  articles  of  every- 
day production. 

But  quite  apart  from  these  practical  applications  of  a  color- 
measure  to  medicine  and  in  the  arts,  it  is  to  be  hoped  that  some 
universal  chromometric  standard  will  finally  be  adopted,  and  so 
there  will  be  added  another  to  that  long  list  of  sciences  whose 
technology  is,  in  the  widest  sense,  the  common  property  of  all 
scientific  men. 


Editorial  in  f 


r)  i.s  so  te 
01  bv  all 


Editorial  in  Fthruary  Cleveland  Journal  of  (Medicine ) 


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